When people need flush corner joints (say, dovetails), I usually see them glue the piece up, sand or plane the joint flush, and then apply stain to the whole thing. That won't work for me, because I want each piece to have a different stain.

I've come up with a few ideas:

Stain the pieces separately before they're glued up, hoping that I don't have to sand through the whole stain to get the joints flush.

Glue the pieces unstained and stain each piece selectively with masking tape, hoping that the stain doesn't seep under the tape and through to the other piece.

Assemble the piece without gluing it, sand the joints flush, disassemble it and stain the pieces separately, and glue it all back up, hoping that all the pieces fit together exactly as before.

All three options seem pretty unlikely to work. Is there a trick to this, or am I going to have to redesign the project to avoid the issue?

I'm using oak and Minwax oil-based penetrating stain, but I'm also interested in solutions for other wood and stain combinations.

1 Answer
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Stain the pieces separately before they're glued up, hoping that I don't have to sand through the whole stain to get the joints flush.

Even the deepest penetrating commercial stains, applied in the normal way, don't allow much sanding so it's best to aim to do almost none after staining if possible. When it comes to flushing joints, even if you only have a 0.008" / 0.2mm discrepancy (!) between one piece and the next you could easily end up sanding through the stain in some areas, so it's almost never feasible.

Glue the pieces unstained and stain each piece selectively with masking tape, hoping that the stain doesn't seep under the tape and through to the other piece.

This is the least likely to work in practice. The idea sounds great on paper but is really only theoretically possible because of the tendency for stains to creep under masks (even under masks much better than common masking tapes) and worse, for the wood itself to wick the stain in unpredictably along the grain lines.

Assemble the piece without gluing it, sand the joints flush, disassemble it and stain the pieces separately, and glue it all back up, hoping that all the pieces fit together exactly as before.

If you go ahead with staining this is actually the way you should be aiming to do this I think — get the piece basically perfect as far as alignment goes, then take it apart, colour the wood as needed and assemble carefully back into alignment.

All three options seem pretty unlikely to work. Is there a trick to this, or am I going to have to redesign the project to avoid the issue?

There is a fourth option, and that's not using stained wood but instead woods that are naturally the colour(s) you want. This is arguably THE way to do something like this and comes with the least in-built hurdles or pitfalls, but the availability and cost of the woods in question can definitely be an issue.